There’s a short section in the documentation about this that may help. There are also some examples in the WordPress page here:
Queries to Set the Sort Order
MapPress by default sorts POIs by title.
You can turn off the default behavior using the shortcode parameter sort to “false”.
If the default sort is turned off, you can use the WordPress order and orderby parameters in queries to sort your posts by various fields including author, date, etc. For example to sort all posts by date, descending:
[mashup query=”orderby=date&order=desc” sort=”false